chan_sip: Access incoming REFER headers in dialplan

This adds a way to access information passed along with SIP headers in
a REFER message that initiates a transfer. Headers matching a dialplan
variable GET_TRANSFERRER_DATA in the transferrer channel are added to
a HASH object TRANSFER_DATA to be accessed with functions HASHKEY and HASH.

The variable GET_TRANSFERRER_DATA is interpreted to be a prefix for
headers that should be put into the hash. If not set, no headers are
included. If set to a string (perhaps 'X-' in a typical case), all headers
starting this string are added. Empty string matches all headers.

If there are multiple of the same header, only the latest occurrence in
the REFER message is available in the hash.

Obviously, the variable GET_TRANSFERRER_DATA must be inherited by the
referrer channel, and should be set with the '_' or '__' prefix.

I avoided a specific reference to SIP or REFER, as in my mind the mechanism
can be generalized to other channel techs.

ASTERISK-27162

Change-Id: I73d7a1e95981693bc59aa0d5093c074b555f708e

diff --git a/CHANGES b/CHANGES
index 4f5225ac1b18def92b1a1f6d549e3985b6e944ae..67d33c95b06e402a6430442d13421417f8ed5523 100644 (file)
--- a/CHANGES
+++ b/CHANGES
@@ -16,6 +16,10 @@ chan_sip
 ------------------
  * New function SIP_HEADERS() enumerates all headers in the incoming INVITE.
 
+ * The variable GET_TRANSFERRER_DATA set in the peer channel causes matching
+   headers be retrieved from the REFER message and made accessible to the
+   dialplan in the hash TRANSFER_DATA.
+
 ------------------------------------------------------------------------------
 --- Functionality changes from Asterisk 14 to Asterisk 15 --------------------
 ------------------------------------------------------------------------------

diff --git a/channels/chan_sip.c b/channels/chan_sip.c
index 941a1e96dc0749e52fe32437f142c7197324dba0..dcfadf4a877be7b2de4d7cd898c71de2638eedd5 100644 (file)
--- a/channels/chan_sip.c
+++ b/channels/chan_sip.c
@@ -377,7 +377,20 @@
                        <para>Since there are several headers (such as Via) which can occur multiple
                        times, SIP_HEADER takes an optional second argument to specify which header with
                        that name to retrieve. Headers start at offset <literal>1</literal>.</para>
-                       <para>Please observe that contents of the SDP (an attachment to the
+                       <para>This function does not access headers from the REFER message if the call
+                       was transferred. To obtain the REFER headers, set the dialplan variable
+                       <variable>GET_TRANSFERRER_DATA</variable> to the prefix of the headers of the
+                       REFER message that you need to access; for example, <literal>X-</literal> to
+                       get all headers starting with <literal>X-</literal>. The variable must be set
+                       before a call to the application that starts the channel that may eventually
+                       transfer back into the dialplan, and must be inherited by that channel, so prefix
+                       it with the <literal>_</literal> or <literal>__</literal> when setting (or
+                       set it in the pre-dial handler executed on the new channel). To get all headers
+                       of the REFER message, set the value to <literal>*</literal>. Headers
+                       are returned in the form of a dialplan hash TRANSFER_DATA, and can be accessed
+                       with the functions <variable>HASHKEYS(TRANSFER_DATA)</variable> and, e. g.,
+                       <variable>HASH(TRANSFER_DATA,X-That-Special-Header)</variable>.</para>
+                       <para>Please also note that contents of the SDP (an attachment to the
                        SIP request) can't be accessed with this function.</para>
                </description>
                <see-also>
@@ -18662,6 +18675,29 @@ static int get_sip_pvt_from_replaces(const char *callid, const char *totag,
        return 0;
 }
 
+static void extract_transferrer_headers(const char *prefix, struct ast_channel *peer, const struct sip_request *req)
+{
+       struct ast_str *pbxvar = ast_str_alloca(120);
+       int i;
+
+       /* The '*' alone matches all headers. */
+       if (strcmp(prefix, "*") == 0) {
+               prefix = "";
+       }
+
+       for (i = 0; i < req->headers; i++) {
+               const char *header = REQ_OFFSET_TO_STR(req, header[i]);
+               if (ast_begins_with(header, prefix)) {
+                       int hdrlen = strcspn(header, " \t:");
+                       const char *val = ast_skip_blanks(header + hdrlen);
+                       if (hdrlen > 0 && *val == ':') {
+                               ast_str_set(&pbxvar, -1, "~HASH~TRANSFER_DATA~%.*s~", hdrlen, header);
+                               pbx_builtin_setvar_helper(peer, ast_str_buffer(pbxvar), ast_skip_blanks(val + 1));
+                       }
+               }
+       }
+}
+
 /*! \brief Call transfer support (the REFER method)
  *     Extracts Refer headers into pvt dialog structure
  *
@@ -18724,10 +18760,18 @@ static int get_refer_info(struct sip_pvt *transferer, struct sip_request *outgoi
 
                peer = ast_channel_bridge_peer(owner_ref);
                if (peer) {
+                       const char *get_xfrdata;
+
                        pbx_builtin_setvar_helper(peer, "SIPREFERRINGCONTEXT",
                                S_OR(transferer->context, NULL));
                        pbx_builtin_setvar_helper(peer, "__SIPREFERREDBYHDR",
                                S_OR(p_referred_by, NULL));
+
+                       ast_channel_lock(peer);
+                       get_xfrdata = pbx_builtin_getvar_helper(peer, "GET_TRANSFERRER_DATA");
+                       if (!ast_strlen_zero(get_xfrdata)) {
+                               extract_transferrer_headers(get_xfrdata, peer, req);
+                       }
                        ast_channel_unlock(peer);
                }